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Forces acting on a member

  1. Mar 6, 2007 #1
    1. The problem statement, all variables and given/known data

    A block with a mass of 150kg is supported by a cable which passes over a 150 mm diameter pulley that is attached to a frame. Determine all forces acting on member BCD of the frame.

    The distance from A to B is 600mm, and the distance from A to C(just horizontal distance) is 400mm. Distance from A to D is 450mm. Also, the cable is at a 70 degree angle from the +y axis(or a 20 degree angle from the x).

    2. Relevant equations



    3. The attempt at a solution

    Me and a buddy, are stuck on this. We are having a hard time with these type of problems. Need a walk though(real slow). I drew a free body diagram.

    I've got forces on A(Ax and Ay), B(Bx and By), D(Dx and Dy). Also the pulley with a tension(T). Am I missing anything?

    I don't understand how to solve these type of problems. In class, we usually make a lot of equations with unknowns...and then solve from the unknowns. This is usually done by summing forces in the x and y direction and then also taking moments about a few points(I think). I'm not sure what to use though....Please help....I'm falling behind.

    Thanks,
    Brad
     
  2. jcsd
  3. Mar 6, 2007 #2
    I wish i could help, if you could scan the problem or even rough sketch using Paint, it would help. Include on it your proposed forces, and you will get much greater response.
     
  4. Mar 6, 2007 #3
    haha......crap.....I forgot to post my crappy image from paint. I wish I had a scanner.....but the paint will have to work.

    View attachment supported weight.bmp
     
  5. Mar 6, 2007 #4
    I guess we all need to hope the members remain at rest til the paint image passes muster.
     
  6. Mar 7, 2007 #5
    Ok, my picture got approved. The 3 things on the left side are just attached to like a wall(doesn't much matter, but just wanted you to know, so it wouldn't look like a member).

    Again, I have no clue if my free body is right, nor where to start(seems like way to many variables...too overwhelming for me).
     
  7. Mar 7, 2007 #6
    So now please post the magnitude and assigned directions for all the forces you mentioned up above.
     
  8. Mar 7, 2007 #7
    I don't really have directions(other than the ones I assigned in my diagram). Direction doesn't really matter but I have both Ax and Dx pointing to the right. And Ay and Dy pointing upwards. Bx and By(on member AB) Bx is towards the left, and By is pointing down. On member/point E, I just have tension T.

    I don't have any magnitudes, as I'm stuck there. All I have is the lengths, and the weight hanging.

    Is this any help yet?
     
  9. Mar 7, 2007 #8
    So you have tension, then what is the force on the pulley, and in turn on the diagonal member, then the torque on the horizontal member, etc. post some numbers if you can.
     
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